Conventionally, there are fluid measurement devices for measuring the flow rate of a fluid by utilizing a propagation time over which an ultrasonic signal propagates through a conduit. For example, one such known fluid measurement device is a flow meter device disclosed in Patent Literature 1.
As shown in FIG. 7, in the flow meter device, a first vibrator 32 and a second vibrator 33 are provided on a passage 31. A timekeeper 39 measures a time over which an ultrasonic signal propagates between the vibrators 32 and 33. A flow rate calculator 40 corrects the propagation time of the ultrasonic signal by using an offset value that is stored in advance in an offset memory 41, and calculates the flow rate of the fluid passing through the passage 31 based on the corrected propagation time.
Specifically, ideally, in a case where there is no flow of the fluid in the passage 31, the propagation time of the ultrasonic signal when the ultrasonic signal propagates in a forward direction from the vibrator 32 to the vibrator 33 coincides with the propagation time of the ultrasonic signal when the ultrasonic signal propagates in a reverse direction from the vibrator 33 to the vibrator 32. However, a difference between the propagation time in the forward direction and the propagation time in the reverse direction (i.e., an offset value) may occur due to, for example, characteristic differences between the vibrators 32 and 33. Therefore, by correcting the propagation time by using the offset value, a more precise flow rate can be obtained.